It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) or outside (outboard) the hull. The drive shaft of the water jet apparatus is coupled to the output shaft of the motor. The impeller is mounted on the drive shaft and installed in a housing, the interior surface of which defines a water tunnel. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel. The reaction force propels the boat forward.
The reaction force can be increased by increasing the speed at which the water jet exits the housing. One technique for accomplishing this is to form the exit portion of the housing in the shape of a nozzle having a convergent passageway which further accelerates the water flow therethrough. This type of nozzle is typically referred to as a thrust nozzle.
In order to provide horizontal directional control for the boat, the emerging water jet is diverted from its precisely rearward flow direction. This diversion is typically accomplished by means of a steering nozzle which is pivotably mounted to the housing in flow communication with the exit nozzle outlet. The pivot axis of the steering nozzle is preferably generally orthogonal to the centerline axis of the exit nozzle. The steering nozzle is typically steered remotely by the boat operator via control rods or cables which are coupled to the steering nozzle by control linkages. The steering nozzle may be pivoted horizontally in either direction to the desired extent to achieve the desired steering effect.
For example, U.S. Pat. No. 3,089,454 discloses a water jet propulsion system comprising a jet-producing nozzle which is surrounded by a housing consisting of two companion members, which are bolted together along adjacent flanges. The companion housing members form an open housing constituting a substantial portion of a hollow sphere. A jet-directing member for steering has an inner or forward portion which also forms part of a hollow sphere concentric with the housing and is rotatable within in the housing in the manner of a ball-and-socket arrangement. This inner or forward portion of the jet-directing member is pivotably mounted by means of a pair of diametrally opposite, radially extending pivot shafts rotatably mounted in the housing. The jet-directing member is pivotable to a limited extent on an axis perpendicular to the axis of the discharging end of the nozzle. A steering arm controls the positioning of the jet-directing member during steering.
In addition to steering, it is frequently desirable to control or change the boat's attitude. This can be accomplished, for example, by providing means for enabling the steering nozzle to pivot about a horizontal axis. This vertical pivoting action is similar to the horizontal pivoting action previously described, except that the range of vertical pivoting needed to provide the desired change in attitude (i.e., trim) angle is typically only about 20 degrees.
A water jet propulsion system having a jet nozzle with both horizontal and vertical pivoting action is disclosed in U.S. Pat. No. 3,776,173. In accordance with this system, the water flows through a housing which terminates in a substantially hemispherical flared portion. The spherical portion of the housing encloses a jet nozzle having a constricting passageway that accelerates the water flow. The nozzle comprises a substantially spherically configured bearing surface that is partially enclosed by and concentric with the flared hemispherical housing portion, the latter bearing against the nozzle bearing surface during rotation of the nozzle. The nozzle can rotate about mutually orthogonal pivot axes to achieve steering and attitude control respectively. During these rotations, the nozzle and flared housing portion behave in the manner of a ball and socket, except that the hemispherical flared housing portion only encloses part of and does not capture the nozzle.
There is a need for an articulated nozzle assembly having a convergent nozzle which can be rotated for both steering and attitude control, but which has a simple construction.